高中物理题
1.Howisthegravitationalforcebetweentwomassiveobjectssimilartoanddifferentfromtheelectricforcebetweentwochargedobjects?
2.Placeafridgemagnet(F)onthedoorofarefrigerator(R).HowdoweknowthatF,butnotR,isthesourceofapermanentmagneticfield?Youmaywanttoexperimentwithsomepins,staples,orpaperclipstoproveyourpoint.
3.Supposeatoneinstantthatamediumsuchasastringappearsflat.Doesthismeanthattherearenowavespropagatinginthemedium?
麻烦各位用英文来解释答案